Identifying Metal-Halogen Bonding for Hydrogen-Induced Acid Generation in Bifunctional Catalysis

Within conventional bifunctional catalysts, active metal sites are associated with metal components, while acid sites are usually localized over oxide supports. The modification of metal sites by halogens provides an opportunity to generate acidity via the heterolytic dissociation of hydrogen directly over metal sites. Herein, we report the results of high-throughput screening of the combinations of different metals (Co, Ni, Ru, Pt, Pd, Rh) and halogens (Cl, Br, I) for acid site generation from hydrogen in the hydrogenation of furfural and 5-hydroxymethylfurfural. The results demonstrate that only Pd and Pt catalysts demonstrate the formation of acid sites by interaction with Br, Cl, and I. The characterization in combination with density functional theory (DFT) modeling indicates hydrogen heterolytic dissociation over halogens localized at the edges and corners of Pd and Pt nanoparticles with an increase in strength of the acid sites with an increase of electronegativity of the halogen.